Prior art methods of patterning (etching or plating) surfaces with micron or sub-micron features include irradiative lithographic methods such as photolithography, electron-beam lithography, and x-ray lithography. The equipment used in conventional irradiative lithographic methods do not easily form large-area devices; they are limited to the fabrication of small-area devices which must subsequently be stitched together if a large-area device is to be fabricated. Typically, the largest area field that can presently be fabricated by a panel printer has a maximum area of about 12 in.sup.2, and a typical photolithographic printer for semiconductor applications has a field area on the order of 1 in.sup.2. The stitching process is costly and time-consuming.
Accordingly, there exists a need for an improved apparatus and method for patterning large area surfaces with sub-micron features, which easily, economically, and reproducibly prints large-area devices, thereby providing high throughput.
Photolithographic aligners are known in the art. They are designed to align hard masks, which are rigid and planar. This is accomplished by aligning one or more alignment patterns on the hard mask with the corresponding one or more alignment patterns on the surface to be patterned. Thus, the pattern on the mask is brought into registration with the pattern on the surface. The alignment is accomplished by making the necessary displacements of the entire hard mask. Since the hard mask is not deformable, it does not tend to bow or otherwise mechanically distort in a manner which can distort the pattern of the mask.
The alignment and contact printing process in photolithographic equipment includes several steps. The mask is placed in a photomask holder. The substrate to be patterned, or wafer, is placed on a vacuum chuck, which includes a plate having holes in it. When the article is placed on a surface of the vacuum chuck, it is held in place by suction through the holes in the plate. The hard mask is then positioned above, and parallel to, the wafer, within several hundred microns. A prealignment is performed wherein one or more alignment patterns on the hard mask are brought into registration with one or more corresponding alignment patterns on the surface of the article. Depending on the geometry of the corresponding patterns, one or two pairs of alignment patterns are sufficient to bring the stamp printing pattern into registration with the overall wafer pattern. One or two pairs of alignment patterns are sufficient to provide alignment regardless of the size of the mask because the mask is rigid. The alignment is accomplished by detecting the relative positions of the alignment patterns and making the necessary adjustments in the position of the hard mask and/or wafer by making x-y adjustments and angular/rotational adjustments in position. When alignment is achieved, the hard mask and article are brought into contact. The printing gap between the mask and wafer is about 0-50 micrometers: hard contact is achieved by providing a high vacuum between the mask and wafer; soft contact is achieved by providing a low vacuum, about 50-500 mm Hg. It is recognized in the art that abrupt pressure change to vacuum conditions can trap gas between the mask and wafer. However, the solution is generally a step change from large-gap/high-pressure to soft-contact/low pressure followed by a delay for gas release through a valve; thereafter, hard-contact/vacuum are provided by dialing in the desired distance and, optionally, by flowing a stream of inert gas, at a given flow rate, from the underside of the wafer on the wafer chuck.
Micro-contact printing of self-assembled molecular monolayers (SAMs) is known in the art. The SAMs are comprised of molecules, which have a functional group that binds to certain types of solids. The remainder of the molecule (usually a long-chained hydrocarbon) interacts with neighboring molecules to form a dense structure which is impenetrable by certain chemical species. Current micro-contact printing methods for producing a SAM on a surface cannot reliably or reproducibly print surfaces, particularly large-area surfaces having surface areas greater than about 1 in.sup.2.
Accordingly, another purpose of the present invention is to provide a cost-effective, reproducible method for patterning large-area surfaces using micro-contact printing of self-assembled molecular monolayers.